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476 Transactions of S.M.P.E., Vol, XIII, No. 38, 1929
rounding worlds — took exposures from three hours and fifteen minutes, to four hours per frame ; or we might say the average exposure was three and one-half hours per frame. The sun we photographed at normal exposure. The moon, which we photographed when full in order to get the maximum light volume, took seventeen minutes exposure per frame. The planets surrounding our sun varied directly in relation to their distance and the color of light being given off from them. For instance, Mars, which has a red glow, photographs fairly fast as compared to Uranus, which has a pale green glow. Mercury is one of the hardest of our planets to photograph, due to the fact that it lies in a path between us (the earth) and the sun, and the light from the sun can only be overcome at certain seasons and times. The other planets, except Neptune which has a pale blue glow, photograph fairly fast ; however this color value of Neptune is offset by its tremendous distance from the earth.
It was necessary to use the hydrogen filter in all our photographing, as we found this was the only filter that would photograph through the gasses of atmosphere and water vapor which surrounds a lot of the objects we were photographing.
Our process of photographing the heavens which we have recorded (incidently they are the only authentic records on motion picture film of these different bodies) took over a period of fourteen months. We worked every night through the different telescopes on Mount Wilson, California.
The work was made possible only by the fine co-operation that was given us by the Carnegie Institute of Washington, D.C., and the untiring efforts of Dr. Adams, Professor Joy, and Professor Ellermen, of the Mount Wilson observatory staff.
In photographing the heavens, it was necessary to focus the object from the ground glass of the telescope through a wide angle lens in the camera, which necessitated incorporating the camera in the body of the base of this enormous telescope at that point where the eye piece prisms are attached for viewing. This meant that the camera had to be left in the telescope for many months. The only camera w^e could get into this small space was a Universal which served the purpose very well due to the fact that it was all stopmotion work.
Before looking at the pictures, I would like to draw your attention to the uneveness of rotation in some of the heavenly bodies. This is caused by the stop motion and long exposures ; the change from one night to another in photographing time ; and the continual movement of the object being photographed.